CN115151662A

CN115151662A - Method for inductive hardening of a surface layer

Info

Publication number: CN115151662A
Application number: CN202180015791.3A
Authority: CN
Inventors: 斯特凡·达彭; 迈克尔·达维多维奇
Original assignee: SMS Elotherm GmbH
Current assignee: SMS Elotherm GmbH
Priority date: 2020-02-20
Filing date: 2021-02-22
Publication date: 2022-10-04
Also published as: WO2021165532A1; US20230082585A1; MX2022010285A; EP4107296A1; JP2023508238A

Abstract

The invention relates to a method for the induction case hardening of a surface (2 a) surrounding an annular component made of hardenable steel, which achieves a uniform and uninterrupted hardening. For this purpose a) the initial zone is brought to the hardening temperature by means of an inductor (1 a, 1b, 3a, 3 b) and quenched by means of a shower device (1 c, 3 c). Then b) hardening the surface (2 a) by means of the stationary inductor assembly (1) and the movable inductor assembly (1, 3), wherein the movable inductor assembly (3) is moved along the surface (2 a) and simultaneously the annular member (2) is rotated around the rotation axis (X) to move the surface (2 a) to be hardened along the stationary inductor assembly (1), wherein the movable inductor assembly (3) is moved along the surface (2 a) with a speed (V2) which is greater than the circumferential speed (V1) thereof. Then c) hardening the end zone (E) of the surface (2 a), so that at least one leading sensor (1 a, 3 a) which first reaches the end zone (E) preheats the end zone (E) until the trailing sensor (1 b, 3 b) is located in the end zone (E) and finally heats the end zone (E) to the hardening temperature. The finally heated end zone (E) is then quenched by means of a spray device (1 c, 3c, 5).

Description

Method for inductive hardening of a surface layer

Technical Field

The invention relates to a method for induction hardening a surface surrounding an annular component made of hardenable steel.

Background

"method for the induction hardening of a skin layer" means a method in which a skin layer of a steel material adjoining the respective face to be hardened is heated to a hardening temperature by means of an electromagnetic field induced in the component, wherein the component carrying the face in each case is made of the steel material, and wherein the skin layer sections which have been heated in this way are subsequently cooled sufficiently rapidly by applying a suitable quenching agent in order to produce a hardened structure in the relevant skin layer section.

Technical and physical background on induction case hardening is in handbook 236"

von Stahl-

(Heat treatment of Steel-case hardening) ",2009 edition, published by the iron and Steel trade Association, sohnstra β e 65, 40237Dsseldorf, and available at URL https:// www.stahl-only.de/wp-content/uploads/2019/04/MB 236_ Waermebedlung _ von _ Stahl _ Randschthichhatten.pdf, available date 2020Download 2 months and 6 days.

The annular component, the surface of which can be hard-skinned using the method according to the invention, is typically a bearing ring for large roller bearings and the like. Such bearing rings are used, for example, for roller bearings for supporting rotors of large wind power installations or for supporting tower cranes or the like in a rotatable manner about a vertical axis. The diameter of such bearings is typically in the range of 40-1000 cm.

The circumferential surface of such a large annular component can be surface hardened particularly effectively by using two inductors which are moved in a synchronous, opposing manner along the surface to be hardened. In this way, the inductor successively heats the respective surface section covered by the electromagnetic field generated thereby to the hardening temperature. The surface sections heated in this way are then quenched by spray jets which are emitted by spray devices guided correspondingly downstream of the inductors.

In contrast to the advantage of this type of case hardening, two or more inductors can each only be moved close to one another to a certain distance, because of the structural space they occupy. In this way, even if the inductors are arranged in the closest vicinity at the beginning or end of the machining operation, there remains a region on the workpiece in which only insufficient hardness is achieved, since the electromagnetic field generated by the inductors does not reach directly into the region of the surface to be hardened which is present between the inductors or is heated only insufficiently due to the mutual interference of the fields generated by the inductors. In practice, it has proved to be less problematic in the initial region of the surface to be hardened above which the inductor is immediately adjacent at the beginning of the hardening process than in the end region, since the previously heated surface section does not have to be quenched at the same time as the initial region is heated, and therefore there is sufficient time for the region not directly swept over by the electromagnetic field of the inductor to also reach the hardening temperature by thermal migration.

However, if no special countermeasures are taken, there remains in the end region of the surface to be hardened, in which the inductors meet again after moving along the ring segment assigned thereto, a region which is insufficiently heated and therefore does not reach the hardness achieved in the remaining section of the surface to be skin-hardened due to the structural conditions. Such regions which are only incompletely hardened are also referred to in technical terms as "gaps" (Schlupf) and can lead to premature failure in practical use, in particular in applications in which the hardened face of the skin is regularly loaded over its entire circumference. Due to its lower hardness, the notch region wears out more quickly than the remaining, more hardened region of the hardened surface of the skin layer.

Various methods have been developed to achieve unnotched hardening of the surrounding faces of large annular components.

A first example of such a method is known from EP 1 848 833 B1. In the method for producing a bearing ring for a large roller bearing having at least one raceway with a hardened surface layer, at least two inductors are arranged at the beginning of the hardening above a common initial region of the annular raceway to be hardened and the opposite surface layer is heated there to a hardening temperature. The inductor is then moved in the opposite direction along the raceway to heat the intermediate region of the annular raceway of the bearing ring associated with the initial region, respectively. After a short distance of the inductors moving in opposite directions to each other, the shower arrangement towards the heated surface layer is switched on, so that the associated previously heated surface layer begins to quench from the centre of the initially heated zone. The sensor and the associated spray device are then moved further on their half-rings until they meet again in an end zone opposite the starting point and form a common heating zone there again. After the finish area reaches the desired hardening temperature, the two inductors rise vertically from the raceway surface, freeing up space for the spray device, which is now directed at the finish area to quench it. In order to bring the end zone reliably and quickly to the hardening temperature, the known method provides an additional auxiliary inductor which already preheats the end zone when heating the initial zone or the intermediate zone.

Another known EP 2 310 543 B1 is a method of the type in question. This method is based on the old method described in EP 1 848 833 B1 and provides that the auxiliary inductor used for preheating the end zone in the method known from EP 1 848 833 B1 is moved with an additional degree of freedom, such as wobbling or hovering, compared to the movement set in the old method to homogenize the heating.

A third method for hardening workpieces, such as bearing rings or toothed rings, which describe a closed curve, is known from EP 1 977 020 B1. In the known method, in a first working step, at least two sensors are attached to the workpiece in a starting region, wherein the sensors occupy starting positions which are immediately adjacent to one another and which define a starting region therebetween. The initial zone is then heated to a hardening temperature by at least one of the inductors and then quenched. The inductors are then moved along the workpiece starting from their respective starting positions, wherein the direction of movement of one inductor is opposite to the direction of movement of the other inductor, and wherein the sections of the workpiece which are respectively located within the effective range of the inductors are heated to a hardening temperature and then quenched. The opposite movement of the inductor continues until the inductor reaches an end position in which it is in close proximity to the respective other inductor. An end zone is now enclosed between the end positions reached by the two sensors. In order to also bring it to the hardening temperature, the inductors are moved together in the direction of one of the moving directions of the inductors, and the end zone is heated to the hardening temperature by the inductor which has previously moved in this moving direction. In this way, the end zone is completely passed by at least one of the inductors and is uniformly brought to the hardening temperature.

Finally, EP 2 542 707 B1 discloses a method and a device for the induction hardening of an annular surface of a round component, wherein four inductors grouped into two inductor pairs are arranged on the annular surface to be hardened, wherein each inductor pair is assigned a spray device, and the spray devices are arranged closely next to one another at the start of heating. The inductors of the inductor pair and the corresponding spray devices are also arranged directly next to one another. The inductor-spray device combination oriented in this way in the initial region of the track to be hardened is moved in the opposite circumferential direction after switching on along the respectively corresponding intermediate section of the track to be hardened, so that the surface section previously heated to the hardening temperature by means of the inductor is subsequently immediately quenched to form a hardened structure on the surface of the track. The pairs of inductors continue their reverse movement until the respective leading inductors of the pair meet at the end zone of the raceway. When the ending region is reached, the leading sensor is removed from the rolling surface to make room for the trailing sensor of the sensor pair. These trailing inductors are moved further in their respective current circumferential direction until they also meet above the end zone, and the end zone is also heated to the hardening temperature by the two trailing inductors. After the trailing inductors together with their respectively assigned spray devices have also been moved away from the end region of the surface to be hardened, either sequentially or simultaneously, the end region is also quenched by a further spray device in order to likewise obtain a hardened structure there.

Disclosure of Invention

Against the background of the prior art described above, the object of the invention is to provide a method which is optimized with regard to time requirements and which makes it possible to optimally harden the circumferential surface of the annular component uniformly and without interruptions.

The invention achieves this object by means of a method in which at least the operating steps given in claim 1 are carried out.

It is self-evident here that the person skilled in the art, when carrying out the method according to the invention and the variants and further developments thereof set forth herein, supplements the working steps not explicitly mentioned here, which the person skilled in the art knows on the basis of his practical experience are usually used when carrying out such a method.

Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below together with the general idea of the invention.

The method according to the invention is used for the inductive case hardening of a surface surrounding an annular component made of hardenable steel, in particular a bearing ring for a large roller bearing, which surface has an initial region that is case hardened at the beginning and an end region that is case hardened at the end. To this end, the method according to the invention comprises the following working steps:

a) Hardening the surface layer of the initial zone by bringing the initial zone to a hardening temperature by means of at least one inductor and quenching by means of at least one spray device directing a jet of quenching medium at the heated initial zone;

b) Subsequent to the case hardening of the initial zone, successive (sukzessiv) case hardening of the surface to be case hardened of the annular component is carried out

By means of two inductor assemblies, each of which comprises a leading inductor, a trailing inductor and a spray device, the leading inductor causing a preheating of the regions of the surface to be case hardened, which regions are respectively swept by the leading inductor, the trailing inductor being arranged offset with respect to the leading inductor in the direction of the initial zone and finally heating the regions previously preheated by the leading inductor to a hardening temperature, the spray device quenching the regions of the surface to be case hardened, which regions are respectively finally heated by the trailing inductor with a jet of a quenching medium,

-wherein one inductor assembly is fixedly arranged,

the other inductor assembly is configured to be movable and to be moved for hardening of the surface along the surface to be hardened of the surface, and

-simultaneously, rotating the annular member about an axis of rotation to move the face to be case hardened along the stationary inductor assembly, wherein the speed of movement of the movable inductor assembly along the face to be case hardened is greater than the peripheral speed of the face to be case hardened of the annular member;

c) Hardening the end zone in that the leading inductor of at least one of the inductor assemblies is moved at least temporarily in the direction of the end zone at an increased feed speed relative to the trailing inductor of the inductor assembly when the end zone is at a specific distance from the inductor assembly, so that an increased distance is produced between the associated leading inductor and the corresponding trailing inductor, and the leading inductor is located in the end zone at a time interval which is equal to the time interval required for the trailing inductor to overcome the previously produced distance between the leading inductor and the leading inductor, so that the at least one leading inductor which first reaches the end zone preheats the end zone until the trailing inductor of its inductor assembly is located in the end zone and finally heats the end zone to the hardening temperature, wherein the end zone which has finally been heated to the hardening temperature is then quenched by means of a shower device.

Here, two intermediate zones are present between the initial zone and the end zone of the face to be hardened, wherein a first intermediate zone is connected to the initial zone in a first circumferential direction and wherein a second intermediate zone is connected to the initial zone in a second circumferential direction opposite to the first circumferential direction, so that the end zone extends between the ends of the intermediate zones facing away from the initial zone. These intermediate zones are swept over by the inductor assembly used according to the invention during hardening of the skin due to the movement performed by the movable inductor assembly and the simultaneous rotation of the annular member.

In the method according to the invention, the end region of the surface to be case-hardened is thus preheated by means of at least one of the inductors which already participates in the case hardening in the revolution of the middle region of the surface.

Due to its higher feed speed from a certain point towards the end zone, the preceding inductor traveling towards the end zone reaches the end zone of the surface to be hardened faster, so that it can already preheat the end zone as long as the trailing inductor of its inductor assembly is still on the way to the end zone or the end zone is on the way to the respective trailing inductor. If the trailing inductor then reaches the ending region or the ending region reaches the trailing inductor, the leading inductor is moved away from the ending region and the trailing inductor is brought into its position to finally heat the ending region to the hardening temperature. If the end zone reaches the hardening temperature, the trailing inductor can also be removed from the end zone and the end zone can be quenched by means of a spray device provided for this purpose. Alternatively, the end zone can also be moved to a spray device in order to carry out the quenching.

The moving inductor assembly moves along the circumferential surface to be hardened, also moving at a circumferential speed, at a feed speed greater than the circumferential speed of the circumferential surface, so that the moving inductor assembly leads the circumferential surface. The movement of the movable inductor assembly along the rotating circumferential surface to be case hardened and the direction of rotation of the circumferential surface to be case hardened are correspondingly co-directional.

The leading sensor of the moving sensor arrangement is arranged in front of the trailing sensor in the feed direction, behind which the shower of the sensor arrangement is positioned, viewed in the feed direction. In this way, successive new unhardened regions of the circumferential surface to be skin-hardened reach the region of action of the electromagnetic field induced by the leading inductor of the moving inductor assembly, are thus preheated and then reach without interruption the region of action of the electromagnetic field induced by the trailing inductor of the moving inductor assembly. By means of this field, the respective covered region of the surface to be case hardened is finally heated to the hardening temperature in order then to be quenched by the spray device of the moving inductor assembly.

In the fixed inductor assembly, the leading inductor is arranged offset with respect to the trailing inductor with respect to the direction of rotation of the circumferential surface of the ring component, so that, as a result of the rotational movement of the ring component, the respective unhardened region of the surface to be case hardened (that is to say the region of the intermediate region existing between the initial region and the end region) successively reaches the region of action of the electromagnetic field of the leading inductor ("preheating inductor") and subsequently of the trailing inductor ("final heating inductor") of the fixed inductor assembly in order to be subsequently quenched by the shower device corresponding to the fixed inductor assembly, which is arranged behind the trailing inductor of the fixed inductor assembly with respect to the direction of rotation of the ring component.

By keeping the feed speed of the stationary inductor assembly constant equal to twice the peripheral speed of the circumferential surface of the annular member to be hardened, a symmetrical hardening of the intermediate zone can be achieved. In this case, the leading sensor of the moving sensor arrangement can move after reaching its distance from the end zone, which is set as its acceleration starting point, at a speed which is further increased relative to the feed speed of the movable sensor arrangement maintained up to this point in the direction of the end zone, while the trailing sensor of the moving sensor arrangement and the shower continue to move at the feed speed which was maintained up to this point in the past.

As an alternative or in addition to the advance sensor of the moving sensor assembly performing an accelerated feed movement when the distance to the end zone set for this purpose is reached, the advance sensor of the stationary sensor assembly can also move toward the end zone, in this case counter to the direction of rotation of the circumferential surface to be hardened, as soon as the end zone is at a distance from the advance sensor set for the start of the movement.

In the case where both the leading sensors of the moving sensor unit and the leading sensors of the fixed sensor unit move toward the end area, the leading sensors preferably move toward each other at the same speed. In this way, the leading inductors meet above the end zone in order then to heat the end zone jointly. For this purpose, the direction of movement of the leading sensors of the stationary sensor assembly is reversed after reaching the end zone, and the two leading sensors of the stationary and movable sensor assemblies are jointly fed at a speed which is set such that no relative movement occurs between the end zone and the leading sensors, so that the leading sensors constantly rest on the end zone of the circumferential surface to be hardened and in this way jointly uniformly preheat the end zone.

Since the rotation of the annular component on the one hand and the advance movement of the trailing inductors of the moving inductor assembly and of the shower device on the other hand are kept constant here, the end zone of the surface to be hardened and these leading inductors approach the trailing inductors of the fixed inductor assembly and, at the same time, from the opposite side, the trailing inductors of the moving inductor assembly approach the end zone. If the trailing sensor of the moving sensor assembly reaches the end zone and the end zone reaches the trailing sensor of the fixed sensor assembly, which remains stationary, the corresponding leading sensor, which is still above the end zone, can be removed in order to make room for the trailing sensor. If the first two leading inductors are positioned above the end zone, the associated leading inductors can be removed one after the other, so that the respective leading inductor still standing above the end zone can continue to heat the end zone until it has likewise to be removed in order to make room for the following trailing inductor of the movable inductor assembly or in order to engage the end zone into the active region of the trailing inductor of the stationary inductor assembly.

In this case, the final heating can likewise take place jointly by the trailing inductors of the inductor assembly or by one of the associated trailing inductors.

In principle, it may be sufficient for the spray device used according to the invention for quenching to direct a single jet of quenching medium at the respective zone to be quenched, provided that the jet is sufficiently strong and the volume of liquid delivered is sufficiently large to extract heat at the required speed from the zone to be hardened. For this purpose, spray devices which simultaneously emit a plurality of individual jets have proven effective in practice in order to reliably and completely apply an amount of quenching medium to the zone to be quenched which is sufficient for removing heat.

The advantage of using only one inductor for preheating and/or final heating of the end zone, respectively, is that no mutual interference of the correspondingly effective electromagnetic fields occurs, which may occur when two inductors jointly heat a zone in close proximity. No special measures for avoiding these disturbances are therefore required. Furthermore, the use of a single inductor for preheating and/or final heating of the end zone allows precise control of the heat introduced into the end zone, so that, for example, a correspondingly precisely designed hardness profile can be achieved in the hardened skin layer.

As an alternative to the above-described variant in which the preheating and final heating of the end zone are carried out with only one inductor each, it is also possible to carry out the preheating and/or final heating jointly with two inductors, respectively, in the case, for example, that the heating to the hardening temperature should be effected as quickly as possible.

In practice, the speed difference between the leading inductor and its corresponding trailing inductor, or between the circumferential surface of the endless member to be hardened and the corresponding leading inductor, each moving at an increased feed speed, is set, for example, such that the usable time period for the preheating finish zone by the leading inductors is 1 to 10s.

In practice, the increased feed speed of the leading inductor suitable for this purpose is in the range of, for example, 240mm/min to 1800mm/min in value, while the feed speed of the trailing inductor, the temporary and leading inductors moving along the intermediate zone may be in the range of 180mm/min to 1200 mm/min. It goes without saying that, within a range preset for the increased feed speed of the leading inductor and the feed speed of the trailing inductor, the respective speeds are selected such that the increased feed speed of the leading inductor is higher than the speed at which the trailing inductor moves.

In practice, the distance measured in the direction of movement of the leading sensors from the start position (from which the respective leading sensor makes a faster feed movement) until the start of the end zone may be 40-300mm.

In order to ensure that the respective leading inductor also generates sufficient heat in the area swept by it during its fast-moving phase, it can be advantageous to increase the electrical power of the inductor leading at an increased feed speed compared to the electrical power of the associated leading inductor when it is moving at the same feed speed as the trailing inductor of its inductor assembly. It may also be advantageous if the leading inductor associated therewith is moved at an increased feed speed, the power of the respective trailing inductor is also adjusted in order to ensure a heat input sufficient for heating to the hardening temperature.

Also in the heating of the initial zone, it is advantageous for the targeted adjustment of the specific hardness profile to use only one inductor. To this end, according to a further variant of the method according to the invention, in working step a), the heating of the initiation zone to the hardening temperature can be carried out conveniently by means of one inductor of one of the inductor assemblies. In this case, a movement process of the participating inductors, which can be carried out in a simple manner in practice, is obtained if the inductor used for heating the initial region is the trailing inductor of one of the inductor assemblies provided according to the invention. In order to make room for the use of the spray device after heating the initial region to the hardening temperature in this case, the trailing inductor for heating the initial region can be moved, in particular abruptly, after heating the initial region to the hardening temperature in the direction of the initial region of the intermediate region corresponding to its inductor assembly, so that the jet of the spray device provided for quenching the initial region can then be directed at the initial region in the space released by removing the inductor.

The spray means for quenching the initial zone or the end zone, respectively, may be a spray means of one of the inductor assemblies. For this purpose, it can be provided that at least the spray device used for this purpose can be moved independently of the inductor, so that it can be moved for quenching the initial region from its spatial correspondence with the inductor in the normal hardening operation into an operating position in which its spray jet impinges optimally on the initial region to be quenched.

However, for the optimization of the transition between the hardening of the initial zone and the hardening of the intermediate zone immediately following it, it may also be advantageous if a separate spray device is provided for quenching the initial zone, the jet and power of which spray device is specifically coordinated with the conditions present in the region of the initial zone.

Also, at least one of the showers directed with the inductor assembly can be used to quench the ending region. For this purpose, it can also be provided that the spray device can be moved independently of the sensors of the respective sensor arrangement, so that the spray device can be moved from its spatial correspondence with the sensors of the respective sensor arrangement into an operating position for quenching the end zone, in which operating position its spray jets optimally impinge on the end zone to be quenched.

Alternatively, however, the best quenching result can also be achieved here with a minimum cost for the spray system for adjusting the inductor assembly by using an additional spray system for the quenching end zone, which is independent of the spray system of the inductor assembly and is in the waiting position during heating of the end zone.

Drawings

The invention is further elucidated below with the aid of the drawings showing embodiments.

Fig. 1 to 9b each show schematically and not to scale in a top view the device for hardening a surface layer in different stages of the method according to the invention.

Detailed Description

The apparatus shown in fig. 1-9 b is used for case hardening the circumferential surface 2a of the bearing ring 2. It comprises an inductor assembly 1, which is fixedly arranged and has a preheating inductor 1a, a final heating inductor 1b and a shower device 1c. In this case, the preheating inductor 1a is arranged in the circumferential direction U on the circumferential surface 2a of the bearing ring 2 to be hardened before the final heating inductor 1 b. The final heating inductor 1b, which is likewise arranged immediately adjacent to the circumferential surface 2a, is again positioned in the circumferential direction U before the shower device 1c, which shower device 1c is arranged radially offset outward with respect to the circumferential surface 2a with respect to the

inductors

1a, 1 b.

Furthermore, the device has a movable second inductor assembly 3, which second inductor assembly 3 is movable along the bearing ring 2 in the circumferential direction U. The second inductor assembly 3 comprises a preheating inductor 3a, a final heating inductor 3b arranged after the preheating inductor 3a in the circumferential direction U, and a shower device 3c arranged after the final heating inductor 3b in the circumferential direction U. In this case, the spray device 3c is positioned offset radially outward with respect to the circumferential surface 2a of the bearing ring 2, so that it is arranged behind the final heating inductor 1b of the stationary inductor assembly 1 with respect to the circumferential surface 2a in a starting position in which the movable inductor assembly 3 is closely adjacent to the stationary inductor assembly 1 (see fig. 1), but can be moved with respect to the circumferential surface 2a along it in front of the spray device 1c of the stationary inductor assembly 1.

The horizontally oriented bearing ring 2 is held during hardening of the surface layer in a workpiece holder 4 which can move the bearing ring rotationally about its vertically oriented central axis X in the circumferential direction U at a circumferential speed V1.

In the starting position, the final heating inductor 3b of the movable inductor assembly 3 is positioned directly next to the final heating inductor 1b of the stationary inductor assembly 1 in the circumferential direction U. The shower device 1c of the stationary inductor assembly 1 is located behind the final heating inductor 3b, radially outwardly offset with respect to the circumferential surface 2 a. The bearing ring 2 is stationary or is operated in a pivoting manner over a small angle in order to homogenize the heat input during heating of the initial region a of the circumferential surface 2a to be hardened. The

inductors

1a, 1b of the fixed inductor assembly 1 and the

inductors

3a, 3b of the movable inductor assembly 3 now heat together the initial region a (fig. 1).

Once the hardening temperature is reached in the initial region a, the bearing ring 2 is rotated in the circumferential direction U about the axis X, so that the circumferential surface 2a moves about the axis X at the circumferential speed V1. The shower 1c of the stationary inductor unit 1 is switched on and quenches the initial zone a moving along it.

At the same time, the preheating

inductors

1a, 3a of the stationary inductor unit 1 and the movable inductor unit 3 are also switched on, and the movable inductor unit 3 is moved along the circumferential surface 2a of the bearing ring 2 in the circumferential direction U at a speed V2. The velocity V2 is twice the peripheral velocity V1 (V2 =2 × V1). Likewise, once the shower device 3c of the movable inductor assembly 3 has passed the final heating inductor 1b of the fixed inductor assembly 1, this shower device 3c is switched on (fig. 2).

During the movement along the circumferential surface 2a, the regions of the circumferential surface 2a which are respectively located in the active region of the inductor unit 3 are successively hardened and quenched. Here, the preheating inductor 3a performs preheating, the final heating inductor 3b finally heats the corresponding region to a hardening temperature, and the shower device 3c quenches the region heated to the hardening temperature, thereby generating a hardened structure in the surface layer adjacent to the circumferential surface 2 a.

At the same time, the preheating inductor 1a of the stationary inductor assembly 1 heats a region of the circumferential surface 2a moving along the preheating inductor 1, which is then finally heated by the final heating inductor 1b of the stationary inductor assembly 1, in order to be subsequently quenched by the shower device 1c of the stationary inductor assembly 1. Due to the double feed speed V2 of the movable inductor assembly 3 relative to the peripheral speed V1, the relative speed between the inductor assembly 3 and the peripheral surface 2 is equal to the peripheral speed V1. The movable inductor assembly 3 is thus moved towards the end zone E of the circumferential surface 2a (fig. 2-4) at the same speed as the end zone E towards the fixed inductor assembly 1.

The successive hardening of the circumferential surface 2a continues until the end zone E of the circumferential surface 2a approaches the preheating inductor 1a of the stationary inductor assembly 1 by a certain distance. From this point on, the preheating inductor 3a of the movable inductor assembly 3 is moved in advance of the final heating inductor 3b of the movable inductor assembly 3 in the direction of the end zone E at an additionally increased feed speed V2' relative to the feed speed V2. At the same time, the preheating inductor 1a of the fixed inductor assembly 1 moves in the opposite direction to the movement of the preheating inductor 3a and the rotational movement of the bearing ring 2 with a speed V1' towards the end zone E, the speed V1' being numerically equal to the speed V2'. The final heating inductor 3b and the shower device 3c and the bearing ring 2 continue to move unchanged during this time. In this way, the preheating

inductors

1a, 3a meet at a position exactly between the

final heating inductors

3b and 1b above the end zone E (fig. 5).

If this position is reached, the two preheating

inductors

1a, 3a are jointly moved in the direction of the fixed final heating inductor 1b at a feed speed which is set such that no relative movement takes place between the preheating

inductors

1a, 3a and the end zone E, while the final heating inductor 3b and the shower device 3c and the bearing ring 2 continue to move unchanged until the inductor 1a is again in its initial fixed position. During this phase of the process, it is possible to, the end zone E is jointly preheated by the preheating

inductors

1a, 3a (fig. 6).

The preheating inductor 3a of the movable inductor assembly 3 is now switched off and moved into a waiting position away from the circumferential surface 2 a. The preheating inductor 3a continues to move at a speed V2' in the direction of the stationary final heating inductor 1b, while the final heating inductor 3b and the shower device 3c and the bearing ring 2 continue to move unchanged until the preheating inductor 3a approaches the final heating inductor 3b (fig. 7).

The preheating inductor 3a is now also switched off and moved into the waiting position, while the movable final heating inductor 3b with the shower arrangement 3c continues to move in the circumferential direction U at a speed V2 towards the fixed final heating inductor 1b, while the bearing ring 2 continues to move at a circumferential speed V1 until the movable final heating inductor 3b is in a position directly adjacent to the fixed final heating inductor 1 b. The movement of the bearing ring 2 is now stopped and the final heating of the end zone E, which is now located precisely below the

final heating inductors

1b, 3b, is jointly carried out by the

final heating inductors

1b, 3b (fig. 8).

Alternatively, it is also possible here to switch off the two preheating

inductors

1a, 3a as soon as they are close to one another and place them in a waiting position, and then continue the movement of the bearing ring 2 and the movable final heating inductor 3b and the shower device 3c until the final heating inductor 3b reaches its position closest to the final heating inductor 1b and positioned above the end zone E.

If the hardening temperature is reached in the end zone E, according to a first variant, the

final heating inductors

1b, 3b are pivoted away from the end zone E and quenched by means of an additional shower device 5 (fig. 9 a), or according to a second variant, the bearing ring 2 is rotated in the circumferential direction U in a rapid gear until the end zone E is arranged below a fixed shower device 1c, which is then quenched (fig. 9 b).

The invention thus provides a method for the inductive case hardening of a surface 2a surrounding an annular component made of hardenable steel, which achieves a uniform and uninterrupted hardening. For this purpose, the initial region a of the surface 2a is surface-hardened by bringing it to the hardening temperature by means of the

inductors

1a, 1b, 3a, 3b and quenching it by the

showers

1c, 3c. Subsequently, the surface 2a is hardened by means of the fixedly arranged inductor assembly 1 and the movably arranged inductor assembly 3, which respectively comprise a leading

inductor

1a, 3a for preheating the area of the surface 2a swept by the latter, a trailing

inductor

1b, 3b, which is biased in the direction of the initial zone a, for finally heating the preheated area to a hardening temperature, and a

shower device

1c, 3c for quenching the finally heated area, wherein the movable inductor assembly 3 is moved along the surface 2a and simultaneously the annular component 2 is rotated about the axis of rotation X in order to move the surface 2a to be hardened along the fixed inductor assembly 1, wherein the speed V2 of the movable inductor assembly 3 along the surface 2a is greater than its peripheral speed V1. The end zone E of the surface 2a is then hardened by temporarily moving the leading

sensor

1a, 3a of one of the sensor assemblies 1, 3 in the direction of the end zone E at an increased feed speed V1', V2' relative to its trailing

sensor

1b, 3b, when the end zone E is at a specific distance from the sensor assemblies 1, 3, so that an increased distance is produced between the leading

sensor

1a, 3a and its trailing

sensor

1b, 3b, and the leading

sensor

1a, 3a is located in the end zone E at a time interval ahead of the trailing

sensor

1b, 3b, which is equal to the time period required for the trailing

sensor

1b, 3b to overcome the distance produced between it and the leading sensor, so that at least one of the leading

sensors

1a, 3a which first reaches the end zone E preheats the end zone E until the trailing

sensor

1b, 3b is located in the end zone E and finally heats the end zone E to the hardening temperature. Finally, the final heated end zone E is quenched by means of the

showers

1c, 3c, 5.

Description of the reference numerals

1. Fixed inductor assembly

Preheating inductor of 1a inductor assembly

1b Final heating inductor of inductor Assembly

Spray device of 1c inductor assembly

2a circumferential surface of the bearing ring 2 to be hardened

2. Bearing ring (= annular component)

3. Movable inductor assembly

Preheating inductor of 3a inductor assembly 3

3b Final heating inductor of inductor Assembly 3

Spraying device of 3c inductor assembly 3

4. Workpiece accommodating part

5. Additional spraying devices

A initial zone of the peripheral surface 2a to be hardened

E end zone of the circumferential surface 2a to be hardened

U circumference direction

V1 circumferential speed of the bearing ring 2

Feed rate of V1' preheat inductor 1a

Velocity of motion of V2 movable inductor assembly 3

Increased feed rate of the V2' preheat inductor 3a

X central axis of vertical orientation of the workpiece receptacle 4

Claims

1. Method for induction case hardening a face (2 a) surrounding an annular component (2) made of hardenable steel, said face having an initial zone (a) which is case hardened at the beginning and an end zone (E) which is case hardened at the end, comprising the following working steps:

a) hardening the surface layer of the initial zone (A) by bringing the initial zone (A) to a hardening temperature by means of at least one inductor (1 a, 1b, 3a, 3 b) and quenching by means of at least one spray device (1 c, 3 c) directing a jet of a quenching medium at the heated initial zone (A);

b) Subsequent to the case hardening of the initial zone (A), a successive case hardening of the face (2 a) of the annular component (2) to be case hardened is carried out

-by means of two inductor assemblies (1, 3) each comprising a leading inductor (1 a, 3 a) which brings about a preheating of the region of the surface (2 a) to be case hardened which is respectively swept by it, a trailing inductor (1 b, 3 b) which is arranged offset with respect to the leading inductors (1 a, 3 a) in the direction of the initial zone (A) and which brings about a final heating of the region previously preheated by the leading inductors (1 a, 3 a) to a hardening temperature, and a shower (1 c, 3 c) which quenches the region of the surface (2 a) to be case hardened which is previously finally heated by the trailing inductors (1 b, 3 b) respectively with a jet of quenching medium,

-wherein one inductor assembly (1) is fixedly arranged,

-the other inductor assembly (3) is configured to be movable and to be moved for case hardening along the face (2 a) to be case hardened, and

-simultaneously, the annular member (2) is rotated about a rotation axis (X) to move the face to be skin hardened (2 a) along the stationary inductor assembly (1), wherein the movable inductor assembly (3) is moved along the face to be skin hardened (2 a) at a speed (V2) greater than the peripheral speed (V1) of the face to be skin hardened (2 a) of the annular member (2);

c) Hardening the end zone (E) in such a way that, when the end zone (E) is at a specific distance from the inductor assemblies (1, 3), the leading inductor (1 a, 3 a) of at least one of the inductor assemblies (1, 3) is moved at least temporarily in the direction of the end zone at an increased feed speed (V1 ', V2') relative to the trailing inductor (1 b, 3 b) of that inductor assembly (1, 3), so that an increased distance is produced between the relevant leading inductor (1 a, 3 a) and its corresponding trailing inductor (1 b, 3 b), and the leading inductor (1 a, 3 a) is located in the end zone (E) at a time interval ahead of the time interval which is equal to the time required for the trailing inductor (1 b, 3 b) to overcome the distance produced before it and the leading inductor, so that the at least one inductor (1 a, 3 a) which reaches the end zone (E) first reaches the end zone (E) until the end zone (E) is heated by the leading inductor (3 b, 3 b) to a final hardening temperature (E), wherein the leading inductor assembly (1 a final hardening zone (E) is heated by means of the end zone (3) and the end zone (E) is heated to a final hardening temperature (E) of the end zone (3).

2. A method according to claim 1, characterized in that the speed (V2) at which the movable inductor assembly (3) is moved along the face (2 a) to be skin hardened is twice the peripheral speed (V1) of the face (2 a) to be skin hardened of the annular member (2).

3. Method according to any of the preceding claims, characterized in that the leading inductor (3 a) of the movable inductor assembly (3) is moved in the direction of the end zone (E) with an increased feed speed (V2') when the end zone (E) is located at a certain distance from the inductor assemblies (1, 3).

4. Method according to any of the preceding claims, characterized in that the leading inductor (1 a) of the fixed inductor assembly (1) is moved towards the end zone (E) against the direction of rotation of the face to be hardened (2 a) when the end zone (E) is located at a certain distance from the inductor assemblies (1, 3).

5. Method according to claims 3 and 4, characterized in that the leading sensors (1 a, 3 a) of the movable and fixed sensor assemblies (1, 3) are moved simultaneously towards the end zone (E) when the end zone (E) is located at a certain distance from the sensor assemblies (1, 3).

6. Method according to claim 5, characterized in that the feed speeds (V1 ', V2') of the leading inductors (1 a, 3 a) are numerically equal.

7. Method according to any of the preceding claims, characterized in that the end zone (E) is quenched by one of the showers (1 c, 3 c) of at least one of the inductor assemblies (1, 3) after final heating to the hardening temperature.

8. Method according to any of the preceding claims, characterized in that the end zone (E) is quenched after final heating to the hardening temperature by means of a separately provided spraying device (5) separate from the inductor assembly (1, 3).

9. Method according to any of the preceding claims, characterized in that the electric power of the inductor (1 a, 3 a) preceding with an increased feed speed (V1 ', V2') is increased compared to the electric power of the associated leading inductor (1 a, 3 a) operating when it moves with the same feed speed (V2) as the trailing inductor (3 b) of its inductor assembly (3).